linux-kernel - Re: [Linux-cachefs] [PATCH 00/67] fscache: Rewrite index API and management system

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Date:   Tue, 19 Oct 2021 10:29:24 -0300
From:   Marc Dionne <marc.dionne@...istor.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, Latchesar Ionkov <lucho@...kov.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        linux-mm@...ck.org, linux-afs@...ts.infradead.org,
        Shyam Prasad N <nspmangalore@...il.com>,
        linux-cifs@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Trond Myklebust <trondmy@...merspace.com>,
        v9fs-developer@...ts.sourceforge.net,
        Ilya Dryomov <idryomov@...il.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        ceph-devel@...r.kernel.org,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        linux-nfs@...r.kernel.org, Jeff Layton <jlayton@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steve French <sfrench@...ba.org>,
        linux-fsdevel@...r.kernel.org, Omar Sandoval <osandov@...ndov.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Anna Schumaker <anna.schumaker@...app.com>
Subject: Re: [Linux-cachefs] [PATCH 00/67] fscache: Rewrite index API and
 management system

On Mon, Oct 18, 2021 at 11:50 AM David Howells <dhowells@...hat.com> wrote:
>
>
> Here's a set of patches that rewrites and simplifies the fscache index API
> to remove the complex operation scheduling and object state machine in
> favour of something much smaller and simpler.  It is built on top of the
> set of patches that removes the old API[1].

Testing this series in our afs test framework, saw the oops pasted below.

cachefiles_begin_operation+0x2d maps to cachefiles/io.c:565, where
object is probably NULL (object->file is at offset 0x28).

Marc
===
BUG: kernel NULL pointer dereference, address: 0000000000000028
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 5 PID: 16607 Comm: ar Tainted: G            E
5.15.0-rc5.kafs_testing+ #37
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.14.0-2.fc34 04/01/2014
RIP: 0010:cachefiles_begin_operation+0x2d/0x80 [cachefiles]
Code: 00 00 55 53 48 83 ec 08 48 8b 47 08 48 83 7f 10 00 48 8b 68 20
74 0c b8 01 00 00 00 48 83 c4 08 5b 5d c3 48 c7 07 a0 12 1b a0 <48> 8b
45 28 48 89 fb 48 85 c0 74 20 48 8d 7d 04 89 74 24 04 e8 3a
RSP: 0018:ffffc90000d33b48 EFLAGS: 00010246
RAX: ffff888014991420 RBX: ffff888100ae9cf0 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff888100ae9cf0
RBP: 0000000000000000 R08: 00000000000006b8 R09: ffff88810e98e000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888014991434
R13: 0000000000000002 R14: ffff888014991420 R15: 0000000000000002
FS:  00007f72d0486b80(0000) GS:ffff888139940000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000028 CR3: 000000007bac8004 CR4: 0000000000770ee0
PKRU: 55555554
Call Trace:
 fscache_begin_operation.part.0+0x1e3/0x210 [fscache]
 netfs_write_begin+0x3fb/0x800 [netfs]
 ? __fscache_use_cookie+0x120/0x200 [fscache]
 afs_write_begin+0x58/0x2c0 [kafs]
 ? __vfs_getxattr+0x2a/0x70
 generic_perform_write+0xb1/0x1b0
 ? file_update_time+0xcf/0x120
 __generic_file_write_iter+0x14c/0x1d0
 generic_file_write_iter+0x5d/0xb0
 afs_file_write+0x73/0xa0 [kafs]
 new_sync_write+0x105/0x180
 vfs_write+0x1cb/0x260
 ksys_write+0x4f/0xc0
 do_syscall_64+0x35/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f72d059a7a7
Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f
1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d
00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
RSP: 002b:00007fffc31942b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 00007f72d059a7a7
RDX: 0000000000000008 RSI: 000055fe42367730 RDI: 0000000000000003
RBP: 000055fe42367730 R08: 0000000000000000 R09: 00007f72d066ca00
R10: 000000000000007c R11: 0000000000000246 R12: 0000000000000008